Previous version was pretty broken.

Roger Peppe (roger peppe <rogpeppe@gmail.com>)
suggested some improvements. 
This version incorporates his suggestions,
and fixes a ton more problems.
Added a set of tests from biogo.llrb.

See http://code.google.com/p/biogo/source/browse/llrb_test.go

Simplified the tests on the way. Who needs gocheck?